With increasing demand for increased battery life for portable hand-held devices like smart phones and tablets, it is important to achieve high power-efficiency for inductor based switching voltage regulators (VRs) in all modes and states. Dynamic current sensing circuits are used for fine grain power management in different switching states and modes. For example, load current sensing data can be used to switch between Pulse Width Modulation (PWM) mode to Pulse Frequency Modulation (PFM) mode at lighter loads. Load current sensing data can also be used for phase-balancing or phase-shedding in multi-phase VRs. Dynamic current sensing is also used for over-current protection of the VR and the load in case of a catastrophic event. This current sensing data can also be used for telemetry.
Presently, for dynamic current sensing of integrated switching VRs, analog circuit techniques are used. These techniques include series sense-resistor scheme, replica sense-FET based current sensing scheme, and inductor DCR (i.e., DC resistance of the inductor) based load current sensing scheme. Each of the above schemes suffers from shortcomings.
For example, series sense-resistor scheme creates an extra conduction power loss in the VR and additional component cost, and replica sense-FET based current sensing scheme is inaccurate, suffers from a challenging integration scheme, and needs high-voltage operational amplifier to match transistor VDS and high resolution Analog-to-Digital Converter (ADC). Inductor DCR based load current sensing requires an on-die Gm-C filter to filter voltage across the load inductor along with tuning and calibration circuits since the value of inductance and its DCR are un-known generating area/power concerns.
As mentioned above, these current sensing solutions are analog in nature and come with an added cost in terms of area, design complexity, and/or power efficiency. These analog schemes also need significant re-design effort when ported over from one process node to another i.e., the analog scheme for current sensing do not scale well with process nodes.